Cognitive cooperative relaying

Previous works about spectrum sharing in licensed band are all based on a default assumption that the secondary users are equipped with cognitive radios, which enable them to accomplish the spectrum sensing and the ensuing spectrum access. Unfortunately, current wireless communication devices generally lack any functionality of cognition. It is rather challenging to enable such wireless devices to share spectrum with licensed primary systems. As a promising solution, in this paper, we propose a scheme called cognitive cooperative relaying, which introduces a kind of intermediate node, i.e., the cognitive relay, who senses the spectrum activity instead of the secondary user and then opportunistically relays the primary or secondary signal so that the transmission rate of the primary link will keep constant, while that of the secondary link will be maximized. The key feature of the proposed scheme is that, the cognitive relay serves as not only an opportunistic relay for either the primary or secondary transmission pair, but also the Spectrum Policy Server. Simulation results show that, in terms of achievable rate of the secondary user, the proposed spectrum sharing scheme significantly outperforms the conventional one where the secondary user is configured with cognitive radio, which validates a new way of spectrum sharing for current wireless system.